In the related art, there are known endoscopes apparatuses that can observe light incident from a distal end face of an inserted portion and light incident from radially outward (for example, see Patent Documents 1 to 4).
The endoscope apparatus in Patent Document 1 performs observation by switching between light from the longitudinal axial direction and the radial direction by means of a switchable mirror.
The endoscope apparatus in Patent Document 2 employs a structure for making light in a common wavelength band incident from the longitudinal direction and radial direction of the inserted portion via separate image-forming optical systems.
The endoscope apparatus in Patent Document 3 perform observation by multiplexing light with different polarization directions by using a polarizing prism.
The endoscope apparatus in Patent Document 4 performs simultaneous observation of light from the longitudinal direction and the radial direction using a hollow quadrangular pyramid mirror.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. HEI-11-137512
Patent Document 2: Japanese Unexamined Patent Application, Publication No. HEI-9-313435
Patent Document 3: Japanese Unexamined Patent Application, Publication No. SHO-61-261713
Patent Document 4: Japanese Unexamined Patent Application, Publication No. HEI-6-27371